Relay system



April 19, 1938. K. H. SOMMERMEYER 2,114,863

RELAY SYSTEM vFiled Feb. 17, 1936 3 Sheets-Sheet l 166 7/65 Q A/ W' A ril 19, 1938. K. H. SOMMERMEYER 2,114,863

' RELAY SYSTEM Filed Feb. 17, 1936 3 Sheets-Sheet 2 65 Z38 I l K/ W IF. I 544 Z65 A l April 19, 1938. i K. H. SOMMERMEYER. 2,114,863

REHAY SYSTEM Filed Feb. 17, 1936 3 Sheets-Sheet 3 J46 a] di) lays.

Patented Apr. 19, 1938 UNITED STATES RELAY SYSTEM Karl H. Scmmermeyer, Evanston, Ill., assignor to G-M Laboratories, Inc, Chicago, 111., a corporation of Illinois Application February 17, 1936, Serial No. 64,263

14 Claims.

The present invention relates generally to circuits for electrical relays, and more particularly to circuits wherein relays of the sensitive DArsonval type are employed to control other re- In certain respects it constitutes an improvement upon the invention of Archie J. Mc-

Master disclosed in his application for patent for improvement in Relay circuits, Ser. No.

54,032, filed Dec. 12, 1935. It, also constitutes an improvement upon the invention disclosed in my copending application for patent for improvement in Relay system, Ser. No. 64,262, filed February 17, 1936.

The DArsonval movement comprises a coil arranged to rotate within a magnetic field about an axis substantially perpendicular to the direction of the lines of magnetic force. A spring holds the coil in a rest position which may, also, be termed the position of zero current or the zero position. Current traversing the coil reacts with the magnetic field and causes the coil'to rotate therein against the torque of the spring to such a position that the torques exe rted by thegcurrent and the spring are equal and opposite. DArsonval movements are widely used in instruments such as electric meters and electric relays. where high accuracy of operation is required and where only small amounts of electric power are available for operating the instruments. When 'DArsonval movements are. used in sensitive relays it is the practice usually to mount one contacting element on the coil structure so that it will move with the coil into engagement with a stationary cqntact element which serves, also, as a stop for-the coil to limit its motion.

Because the DArsonval movement inherently executes a gradual rotation in response to a gradual change of current and because it tends to open contacts opei ated by it at the same value a of coil current as it tends to close them, this type for relay heretofore has been limited in its performance ability. This has been especially true in respect to load handling capacity and life of its contacts. These difliculties have been overcome to a considerable extent by the inventionof Archie J. McMaster described in his application for patent already referred to. In accordance with that invention, the coil of the DArs'onval relay is so interconnected with its load circuit that current from the load circuit is introduced into the coil circuit to increase the contact pressure immediately and abruptly when the contacts close and to cause the contacts to separate by a considerable space immediately in response to a slight-separation of the contacts. The limitations of the DArsonval movement and the advantages of the McMaster energy transfer arrangement are discussed at length inthe aforementioned McMaster application.

- The system described in the McMaster application possesses the disadvantage that variations in the load circuit such as voltage or current fluctuations, load impedance and the like act to impair the accuracy of any operation -of the contacts of the DArsonval relay if the -energy transfer current was flowing in the relay coil just prior to the operation of the contacts.

Further, I have found that when using the energy transfer" arrangement of the McMaster application, the contacts of the DArsonval relay can close safely a much heavier circuit than it can interrupt and that if the relay contacts never are required to open a circuit, they exhibit little deterioration and apparently have indefinite life.

Accordingly, I have provided a system in which a DArsonval relay utilizes the energy transfer principle of the McMaster application already referred to, but in which the load is applied to the contacts only momentarily at the time of closing so that the contact subsequently opens without load, and in which current from the load circuit is introduced to the DArsonval coil only momentarily at the time its contacts first close.

It is an object of the present invention to provide an improved system and mode of operation for DArsonval relays and the like which will improve their accuracy and reliability.

It is a further object of my invention to provide a system and mode of operation for DArsonval relays which will require the DArsonval relay to perform only those functions for which it is best adapted.

It is a further object of my invention to provide a system and mode of operation for relays of the DArsonval type which minimizes the wear and deterioration of the relay contacts.

A still further object is to increase the range of usefulness of relays having DArsonval movements.

These and other objects and advantages of the present invention will become apparent as the description proceeds.

In order better to acquaint those skilled in the art with the-teachings and practice ofthe present invention, I now shall describe certain specific embodiments thereof, reference being had to the iii) accompanying drawings forming a part of this specification and in which:

Fig. 1 is a partly pictorial and partly diagrammatic illustration of a relay system embodying my present invention.

Fig. 2 is an across-the-line diagram illustrating the circuit of Fig. 1.

Fig. 3 pictorially and diagrammatically illustrates another relay system embodying my invention.

Fig. 4 is an across-the-line diagram of the circuits of the system of Fig. 3.

Fig. 5 illustrates another embodiment of my invention.

Fig. 6 is an across-the line diagram of the circuit connections of the system of Fi'T. .5.

Fig. '7 illustrates still another system embodying my present invention.

Fig. 8 is an acrossthe-line diagram of the circuit connections of the system of Fig. '7.

Referring to Fig. 1, a sensitive relay employing a DArsonval movement is indicated generally by the reference numeral II). It comprises a permanent magnet carrying pole' pieces l2 which, together with a suitably mounted iron core piece I3, provide two magnetic'gaps which constitute the field" of the DArsonval movement. A coil 15 is positioned with one side thereof in each of the two air gaps already mentioned, and is supported at each end by pivots in jewels, the upper pivot being indicated at I6. The pivots are supported in metal pivot-bases H and I8 which are suitably secured to the coil as by means of insulating materials and cement. A pair of fine resilient wires l9 extend in loops from the coil to a terminal strip 20 which is mounted on a stationary portion of the relay supporting structure (not fully shown) so as to provide convenient terminals to the coil |5 of the relay. The lower pivot base l8 carries a metal contact supporting strip 2| the opposite ends of which extend substantially radially from the pivot base. Resilient contact strips 22 and 23 of precious metal are carried by the supporting strip 2|, one at each end thereof. Each contact strip is soldered at one end thereof to the support strip 2| near the pivot base and the free end of the contact strip extends along the supporting strip 2| substantially radially from the pivot-base and is spaced slightly from the supporting strip 2|. A pair of stationary contacts 24 and 25 carried by adjusting screws 28 and 29 are adapted to engage the free resilient ends of the contact strips 22 and 23. Secured, also, to the lower pivot base I8 4;; a spiral restoring spring 26. This spiral spr rig may be soldered to the strip 2| and is utilized as a means for making an electrical connection to the moving contact strips 22 and 23. The outer end of the spring 26 is soldered to an adjustable arm 21 which serves as an electrical terminal. This arm 21 may be rotated to adjust the zero position of the relay coil. Thc'contacts 24 and25 may be adjusted by means of their respective adjusting screws 28 and 29 to' determine the amount of rotation required by the coil l5 to bring about an engagement with them of the movable contact strips 22 and 23. Obviously a setting may be provided such that the contacts (as 22 and 24) can engage so as to prevent the restoring spring 26 from bringing the coil l5 into its zero or rest position. Under these circumstances, the contacts 22 and 24 will be normally closed and a certain amount of current through the coil will be required to open them. As the current Increases above this value, the coil will rotate against the restoring force of the spring 26 until it brings the contact 23 into engagement with the other stationary contact 25 which again limits the motion of the coil.

A light sensitive cell, or primary control device 3| together with two resistors 33 and 34 are connected in series with the coil l5 of the D'Arsonval relay. The light senstive cell 3| conveniently may be that particular type of photoelectric cell which will generate its own current in response to lightincident upon its light sensitive surface. Such a cell is known as a selfgenerating or photoelectronic type of photoelectric cell. Preferably, I employ a self-generating cell such as is shown and described in the copending application of Andrew Christy, Ser.

In the system of Fig. 1, the current from the light sensitive cell 3| will pass through the coil l5 of the relay to operate the contacts thereof in accordance with'the value of the illumination on the cell 3|. Obviously, my invention is not limited to the usebf a photoelectric cell or any particular type thereof, but contemplates any system capable of delivering power to a relay for operating it. i

The contacts of the DArsonval relay I control the operation of a latch relay designated generally by the reference numeral 40. This latch relay is more fully described in my co-pending application already mentioned. The latch relay comprises two separate electro-magnets which have independent magnetic circuits, separate coils 43 and 44, separate armatures 45 and 46 and contacts providing separate contact gaps 52, 53,- and 54. These contacts consist of cantilever spring blades which carry contact buttons at their ends'as shown. The armatures are provided with conical restoring springs 55 and 56 which aid the contact springsand tend to move the armatures 45 and 46 into normal positions from which they may be attracted into drawn-up positions by their respective magnets. The two magnets are held in fixed space relationship with each other by a tie bar 51 which preferably is non-magnetic. The armatures 45 and 46 carry non-magnetic extensions 59 and 60 which are configured to have portions 6| and 62 which so interfere with each other that each relay armature when it is in its own-released position latches the other armature in the drawn-up position. These extensions 59 and 60 together with their respective armatures 45 and 46 constitute a latching mechanism which operates as follows:

In Fig. 1, armature 46 is shown in its drawn-up position and armature 45 is shown in itsreleased position. Interfering portion 6| of armature 45 engages portion 62 of the armature 46 so as to prevent the armature 46 from moving to its released position. When coil 43 is energized, armature 45 will move into its drawn-up position and in so doing will cause its portion 6| to slide along portion 62 of armature 46 and off the end of the same. This action releases armature 46 which immediately moves under force of its own springs to its released position and in so doing latches armature 45 in its drawn-up position. In a similar manner, when coil 44 is energized the armatures 45 and 46 will operate to return to the positionsillustrated in Fig. 1 of the drawings.

Contact gap 53 which is operated by armature 45 is arranged to be closed when armature 45 is in its drawn-up position and to be opened when armature 45 is in its released position. Similarly contact gap 54 which is operated by armature 46 is arranged to be closed when that armature is drawn-up and to be opened when that armature is released. Contacts 5| and 52 may be employed for controlling a load circuit or other apparatus in any known manner..

The circuit of Fig. 1 is illustrated more simply in the across-the-line diagram of Fig. 2. The across-the-line-diagram attempts only to show the electrical relations between the various elements of the system and makes no attempt to depict any mechanical relation. Its only purpose is ,to present the electrical circuits in their simplest form. The same reference numerals are used to indicate the same parts in both Figs. 1 and 2.

Referring now to both Figs. 1 and 2, the battery 65 supplies current for energizing the coil 43 and 44-for operating the latch relay 40. A control circuit for the coil 43 extends from the negative terminal of the battery through the contact gap formed by the two contact pieces 23 and 25 of the DArsonvalrelay 0, thence through the contact gap 54 which is operated by the armature 45, thence through the coil 43 itself, thence through the resistor 33 and thence to the positive terminal of the battery.

In the diagram of Fig. 2, the elements of this circuit extend in a line running across the top of the diagram from right to left. Similarly, the control circuit for coil 44 of the latch relay 40 extends from the negative terminal of the battery 55 through the contact gap formed by the two contact pieces 22 and 24 of the DArsonval relay I0, through the contact gap 53 operated by the armature 45 of the latch relay 40 thence through the coil 44 itself and the resistor 34 to the positive terminal of the battery. The coils 43 and 44 are shunted by spark suppressing resistors 61 and 58 respectively.

The DArsonval relay II) when properly adjusted will close only one of its two contact gaps at one time. Consequently the two coils 43 and 44 will not be energized simultaneously. Assume that the armatures 45 and 46 of the latch relay 40 are in the positions shown in Fig. 1 of thedrawings. The contact gap 54 will be closed and the contact gap 53 will be open. Assume, also, that the light sensitive cell 3| is dark and that, therefore, no

' current is flowing therethrough. Therefore, contact pieces 22 and 24 of the DArsonval relay ill will be in engagement. However, inasmuch as the circuit is open at contact gap 53 of the latch relay 40, nothing will happen. When light falls upon the photoelectric cell 3|, the urrent generated will traverse the coil |5 of the DArsonval coil 43.

relay l andthis current in the coil will re-act with the magnetic field of the magnet I I to rotate the coil against the restoring force of the spiral spring 25 in such direction as to separate the contact pieces 22 and 24 and to bring contact piece 23 towards contact piece 25. As the illumination on photoelectric cell 3| increases it brings contact piece 23 into engagement with contact piece 22 to complete the control circuit for This energizes coil 43 causing the armature 45 to move to its drawn-up position.

A small portion of the current which passes.

ently may be referred to as the energy transfer" current in accordance with the terminology of the McMaster application already referred to. This energy transfer current flowing through the photoelectric cell 3| and the coil l5 from the battery generally will be a very small part of the total current drawn from the battery by the coil 43 and its shunt 61, because the .cell 3| and the coil l5 have much higher resistances than the resistor 33. Thus for example cell 3| and coil l5 together, may have a resistance of the order of 1000 ohms and the resistor 33 may be only a fraction of an ohm. The particular value of resistance to be given resistor 33 depends, of course, upon the value of current drawn by the latch relay coil 43 and its shunt 61 and, also, upon the specific value of the resistance of the photoelectric cell 3| and the coil |5 as well as the value of the energy transfer it is desired to pass through the coil l5 from the battery. Generally, I prefer to supply to the DArsonval relay coil |5 from the battery 65 an energy transfer current which is of an order of magnitude of 25% of the current which is required to rotate the coil from the position where contact strip 22 engages contact 24 to the position in which contact strip 23 carried by the coil engages stationary contactpiece 25.

It will be understood that the energy transfer" current supplied from the battery 65 to the coil i5 is added to or superimposed upon the current already in the coil |5 resulting from the illumination of the photoelectric cell 3|. The photoelectric current and the energy transfer current conveniently may be considered as flowing independent of each other with their separate effects superimposed. This is substantially in accordance with accepted electrical theory. Therefore, so far as the coil I5 is concerned, separate current components flow from the photoelectric cell 3| and battery 65 and either add or subtract depending upon the relative directions of their flow through the coil |5. Under the circuit condition now being described with current in the coil 43, the energy transfer and photoelectric components of current are in the same relative direction and, therefore, add. The operation of the contacts of the DArsonval relay does have some effect upon the output of the photoelectric cell 3|; that is, upon the photoelectric component of current in the relay coil l5. This results from the change of circuit conditions resulting from the closing and opening-of contact gaps. However, this effect is very small in the system illustrated in the drawings. Thus, as already has been mentioned, the combined resistance of the photoelectric cell 3| and coil. |5 may be a thousand times or more greater than the resistance of resistor 33. Insofar as the current generated by the photoelectric cell 3| is concerned, the closing of the path through the coil 43 and its shunt 61 merely places the coil 43 and its shunt 61 in parallel with the resistor 33. Therefore, the operation of the contacts can produce no more than a change of something less than a tenth of one percent (a factor of 0.001) in the resistance in series with the photoelectric cell 3| because that would be approximate change resulting from short circuiting the resistor 33 completely.

The energy transfer current which is supplied from the battery 65 to the DArsonval relay coil |5 through the contact gap formed by the contact pieces 23 and 25 of the DArsonval relay in the manner just described, is in such a direction as to tend further to move the contact piece 23 against the stationary contact 25. That is, maintain itself only by forcing current.across the energy transfer current acts to increase the pressure between the contact surfaces of the DArsonval relay I and tends to prevent those contact pieces from separating. It is thusseen that as soon as the contacts of the DArsonval relay close, additional current is supplied from the battery 65 to the relay coil i5 to insure that those contacts remain closed and to insure further that they maintain a low resistance contact.

The urrent through the coil 43 causes the armat e 45 of the latch relay to move into its drawn-up position. When it arrives there, the portion 6| of the extension 59 of the armature 45 dis-engages the portion 62 of the extension 60 of the armature 46, thereby unlatching armature 46 and permitting it to move towards its released position. It is to be observed that the several springs which act to load the armature 46 tend to hold the portion 62 firmly against the end of the portion 6| of the extension 59 of the armature 45. Therefore, as soon as the armature 46 begins to move towards its released position, it acts to "block or latch the armature 45 in its picked-up position. After the armature 46 moves a slight distance it opens the contact gap'54 and in so .doing interrupts the flow of current through they coil 43 and its shunt resistor 61. In so doing, it,

also, interrupts the flow of current from the battery 65 through the photoelectric cell 3| and coil l5 of the D'Arsonval relay. That is, it interrupts the flow of energy transfer current from the battery 65 tothe coil l5 of the DArsonval rela'y;

and it leaves the DArsonval relay in exactly the same condition as it was just prior to the engagement of its contact pieces 23 and 25. The photoelectric current still flows in its coil l5.

When the contact gap 54 opens, it disconnects the battery 65 from the coil 43 so as to terminate the delivery of power thereto. The flux of the magnet oi the coil 43 immediately begins to collapse and in so doing induces a voltage in the coil in the direction of the current. Because of the presence of the shunt 61 across the coil 43,

the armature 45 for a short time after the con-.

tact gap 54 opens so as to give the armature 46 ample time to latch the armature 45 in the event that because of misadjustment or otherwise the contact gap 54 opens before the armature 45 is latched positively.

The shunt resistor 61, also, serves as a spark suppressor for protecting the various contacts, and especially the contacts of the DArsonval relay H! from destructive sparking and arching resulting from the inductive kick of the magnet of the coil 43. The voltage induced in the coil 43 is proportional to the rate oi change of flux, that is the speed of its collapse. flowing through the coil 43 and the shunt 61 retards the collapse of flux (or lowers its rate of change), it, also, prevents the induced voltage from reaching a high value. By lowering the resistance of the shunt 61, the induced voltage or inductive kick can be reduced to any desired value. Without the shunt 61, the flux could Since the current the opening contact gap in the form of an are or spark. While the actual opening of the circuit would take place at contact gap 54 a spark, also, might appear at the contacts of the DArsonval relay as follows:

The initial closing of the DArsonval relay contact gap formed by the contact pieces 2| and 23 produced an abrupt increase in the current in the coil l5. This caused the coil l5 to force the resilient contact strip harder against the stationary contact piece 23. The coil necessarily moved because of theresilience of the contact strip 2| and unless critically damped would move damping (and. there must be some) would prevent it from returning to the starting condition. However, if the time requiredfor the operation of armature 45 and the subsequent releaseof armature 46 should be slightly less than the period of the oscillating coil IS, the energy transfer current in the coil |5 would be interrupted by the opening of the contact gap 54 when the coil I5 was in motion and moving toward the position at which the contact pressure goes to zero and permits the contact pieces 2| and 23 to separate. The coil l5, therefore, would actually move to separate the contact pieces 2| and 23. If these contact pieces should separate while the arc exists in the contact gap 54, another are would draw between the contact pieces 2| and 23 because of the voltage induced by the collapse of flux in the coil 43. While some current necessarily would flow in order to maintain the are or spark and while this would provide some energy transfer current in the coil l5, that current would be small compared to the full curas their circuit is open at the contact gap 54 nothing occurs as a result of their touching. It thus is seen that it is impossible for the contact pieces 23 and 25 of the DArsonval relay Hi to engage with only slight contact pressure and with current passing through them; and it is further seen that it is impossible for these contact pieces to repeatedly open and close their gap under load with a chattering or frying action.

When the illumination on the photoelectric cell 3| again decreases to such a value that the contact pieces 22 and 24 engage, power is supplied from the battery to the coil 44 in a manner similar to that just described for coil 43; A part of the current drawn by the coil 44 and its shunt the contact pieces 22 and 24 engage firmly and with considerable contact pressure. The operation of the latch relay 40 in response to the energizing of coil 44 returns the armatures 45 and 45 to the positions shown in Fig. 1.

It' will be seen from the foregoing description, that the energizing of a coil of the latch relay 40 is under the concurrent dependent control of contacts of both the latch relay itself and contacts of the DArsonval relay I0. Thus the coil 43 is energized under control of the contact gap 54 of the latch relay and the contact gap formed by the contact pieces 23 and 25 of the DArsonval relay. The control of these contacts is dependent in that neither can energize the coil 43 alone. It is concurrent in that the two contact gaps must be closed simultaneously to energize the coil 43. These'two contact gaps, also, are dependent upon each other in supplying current fromthe battery. 65 to the coil I5 of the DArsonval relay. Similarly, the-contact-gap 53 of the latch relay and the gap formed by the contact pieces 22 and 24 of the DArsonval relay constitute another group of contact gaps which are dependent upon each other in supplying power from the battery 85 to either the coil 44 of the latch relay 40 or the coil I5 of the DArsonval relay I0. While the contacts of each of these groups are dependent within the group itself, the two groups act independently in energizing coil I5 from the battery 65.

When employing my present invention with apparatus having an un-symmetrical impedance characteristic, I prefer to choose different values of resistance for the two resistors 33 and 34 so as to provide approximately equal values of energy transfer current for the two operations of the DArsonval relay. Photoelectric cells of the self generating type invariably possess unsymmetrical impedance characteristics. That is, a photoelectric cell of this type will permit different values of current to flow therethrough in response to an impressed voltage depending upon the polarity of the applied voltage with respect to the polarity of the photoelectric cell. In some types of cells, the higher impedance is presented to a current flowing in the same direction as does the photoelectric current; and other types of self-generating cells present their lower impedance to currents in the same direction as the photoelectric current. Thus for example a selfgenerating photoelectric cell employing iron and selenium, such as the one shown and described in the co-pending application of Andrew Christy, Ser. No. 646,627, filed December 10, 1932, already referred to, the higher impedance is presented to a current flowing in the same direction'as the photoelectric current. Accordingly when employing a photoelectric cell of this particular construction in the system of Fig. 1, the resistor 34 is given a lower value than the resistor 33.

Thus when the current is drawn through the coil 43 of the latch relay 40, a comparatively high voltage is impressed upon the photoelectric cell 3| by the voltage drop across the comparatively high resistance of the resistor 33. This passes current through the coil I5 and the photoelectric resistance 34 is impressed upon the photoelectric cell 3| and the coil I5. The current due to this voltage drop flows in the direction opposite to that in which the photoelectric current flows and, therefore, encounters a comparatively low impedance. Obviously, if I should wish to provide a greater energy transfer current in response to the closing of one contact gap of the DArsonval relay than is provided in response to the operation of its other contact gap, the same can be accomplished easily by selecting suitable values for the resistors 33 and 34.

Furthermore, should I wish to employ a photoelectric cell which presentsits higher impedance to currents in the direction opposite to that of the photoelectric current, I may give the resistor 34 a higher resistance value so as .to keep the energy transfer component of current at the desired value for each direction of operation.

In Fig. 3 is illustrated another system embodying my present invention. A DArsonval relay IIO similar to the relay I of Fig 1' has a coil I|5, contact pieces I22 and I24 providing a normally closed contact gap and contact pieces I23 and I25 providing a normally open contact gap. A photoelectric cell I3I similar to the photoelectric cell 3| of Fig. 1 is connected to the coil through an energy transfer resistor; I35. DArsonval relay I II is arrangedto control the operation of a relay I40 having a coil I4I, a normally open contact gap I42 and a pair of load contacts I43. The power for the operation of the relay I40 is supplied from a battery I65 through a current limiting resistor I60. The circuit is more clearly shown in the across-the-' line diagramof Fig. 4. The across-the-line diagram attempts to show only the electrical relation between various elements and makes no attempt to show any mechanical relations diagrammatically. The various elements shown therein may be identified'by the reference numerals from the illustration of Fig. 3. As may be seen more clearly from the diagram of Fig. 4, the normally open contact gap I42 of the relay I40 is connected in series with its coil I 4| and this combination is connected across the combination of the battery I65 and the resistor I66. The two series connected contact gaps of the DArsonval relay IIO formed by the contact pieces I22 and I24 and the pieces I23 and I25 respectively, also, are connected across the combination of the contact gap I42 and coil I4I of the relay I40. An energy transfer resistor I35 shunted by the coil II5 of the DArsonval relay and the photoelectric cell I3I, is bridged between .(1) the connection between the contact gap I42 and the coil I 4| and (2) the connection between the two separate contact gaps of the DArsonval relay IIO. -A spark suppressing shunt resistor I68 is provided for the coil |4| of the relay I40.

The operation of the system of Figs. 3 and 4 is as follows: Assume that the relay I40 is deenergized and that its armature is released so that its contact gap is open as shown in Fig. 3, this being its normal condition; Assume further that the photoelectric cell |3| is receiving sufficient illumination so that the current passed thereby through the coil II5 of the DArsonval relay is of value sufiicient to hold the normally closed contact gap thereof, (the one formed by the contact pieces-l22 and I24) open. If now, the illumination of the photoelectric cell I3I increases to such'a value as to close the normally open contact gap of the DArsonval relay' (the one formed by the contact pieces I23 and I25),

The

nothing will happen because the circuit from the battery is open at both the contact gap I42 of the relay I 46 and the normally closed contact gap of the DArsonval relay which is formed by the contact pieces I22 and I24. When the illumination decreases to such value as to permit the normally closed contact gap oi. the DArsonval relay to close, a circuit is completed thereby as follows:

Extending from the positive terminal of the battery I65 through the normally closed contact gap formed by the contact pieces I 22 and I24 of the DArsonval relay, through the energy transfer resistor I35 through the coil MI and its shunt I68 and the current limiting resistor I66 to the negative terminal of the battery I65. The current flowing in this circuit divides between the energy transfer resistor I35 and its shunt circuit consisting of the coil I I5 and the photoelectric cell I3I to oppose the photoelectric current so as to increase the pressure at the contact surfaces of the D'Arsonval relay.

The current passing through the coil I4I causes the relay I40 to pick-up its armature and close its contact gap I42. This short circuits the current path through the normally closed contact gap of the DArsonval relay and the energy transfer resistor I35 so as to substantially terminate the flow of current therein. This effectively removes the "energy transfer component of current from the coil I I5 of the DArsonval relay I I0 and effectively prevents any voltage drop from thereafter appearing between the contact pieces I22 and I24 when they separate. The contact gap I42 of the relay I4Il acts to electrically lock this relay in its energized position by maintaining its coil circuit. Thereafter the normally closed contact gap of the DArsonval relay formed by the contact pieces I22 and I24 may open and close repeatedly, but no relay operation will result therefrom and substantially no flow of current will be established or interrupted thereby.

Then when the illumination of the photoelectric cell I3I again increases to such a value as to bring the contact pieces I23 and I25 into engagement, they act to short circuit the coil I but the short circuit current flows through the energy transfer resistor I35. This flow of cur-- rent through the resistor I35 is in the direction therethrough opposite to the direction of the current which flowed therein when the relay previously operated so that it produces an "energy transfer component of current in the direction opposite to that supplied when the relay previously operated thereby to increase the total current in the coil H5 and increase the contact pressure of the contact pieces I23 and I25. Under this condition the flow of current from the battery is limited by the current limiting resistor I66. Obviously, if the battery I65 has sufiiciently high internal impedance to sufliciently limit its current the resistor I66 can be eliminated. Short circuiting the coil I4I, that is shunting it with the low impedance path of the resistor I35 and the contacts of the DArsonval relay, so reduces the flow of current through the coil I4I that it releases its armature and causes its contact gap I42 to open. This opens the battery circuit completely so that the flow of current through the resistor I35 and the contacts of the DArsonval relay is terminated. This returns the apparatus to its original condition with the circuit open at the contact gap I42 of the relay I40 and at'the normally closed contact gap of the DArsonval relay (the gap formed by the contact pieces I22 and I24). Therefore, the contact pieces I23 and of the battery 65 illustrated in Fig. 1.

I25 of the normally open contact gap of the DArsonval relay may open and close repeatedly without producing any operation of the apparatus or making or breaking any current.

It will be observed that a greater current flows from the battery when the normally open contact gap of the DArsonval relay (contact pieces I23 and I 25) closes than when its normally closed contact gap (contact pieces I22 and I24) closes because in the first case the current is limited only by the resistor I66 while in the second case it is limited by the resistor I66 and, also, by the coil MI and its shunt resistor I68. However, since the photoelectric cell I3I presents a greater impedance to the flow of current therethrough in the same direction as the photoelectric current flows, the greater voltage drop across the energy transfer resistor 35 encounters a higher impedance in the path through the coil H5 and the photoelectric cell I3I than does the lower voltage drop resulting from the flow of current therethrough in the opposite direction. By suitably choosing the values of the resistance of the coil I and its shunt I68 and the resistor I66, the energy transfer current can be made substantially the same for operation at both contact gaps of the DArsonval relay.

The systems of Figs. 1 and 3 differ somewhat from each other in construction and operational characteristics, and each possesses certain advantages over the other. Thus, the system of Fig. 1 requires less power for its operation because current is drawn from the battery 65 only for a brief instant each time that the latch relay is made to operate; and it is free of any tendency of its armatures and contacts to change their positions in response to a temporary failure of power such as might occur if the power were supplied from a commercial powerline instead The relay I40 of the system of Fig. 3 is somewhat more simple and lower in cost than the latch relay of Fig. 1; and it will release and return to the position in which it is illustrated in response to any failureof the battery to supply sufficient curcent and voltage thereto.

In Fig. 5, is illustrated, a time delay latch relay system generally of the type which is shown and described in my co-pending application already referred to, but employing a DArsonval relay and embodying my present invention therewith for improving the operation of the DArsonval relay. In Fig. 5, the coil 2I5 and contact gaps 231 and 238 of the DArsonval relay are illustrated diagrammatically. The coil H5 is connected in series with a self-generating photoelectric cell 23I and a pair of resistors 233 and 234. The DArsonval relay and the photoelectric cell 23I are connected to control the latchrelay 240. The circuit connections are more clearly shown in the across-the-line diagram of Fig. 6.

The latch relay 240 is similar to the latch relay 40 of Fig. 1 and comprises a pair of magnet coils 243 and 244 having shunt resistors 261 and 266 connected thereto which are similar to the shunt resistors 67 and 68 of Fig. 1. The magnet coil 243 may be energized to operate an armature 245 and similarly the magnet coil 244 serves when energized to operate the armature 246. The armature 245 operates a three-blade assembly of contacts providing two contact gaps 253 and 255. The contact gap 253 is arranged to be open when the armature 245 is in its drawn-up position.

. battery 265.

than the current through coil 244. The resistors armature 245 is in its drawn-up position. Similarly, the armature 246 operates a 3 blade assembly of contacts providing contact gaps 254 and 256, of which, contact gap 254 is open and contact gap 256 is closed when the armature 246 is in its drawn-up position. Jidditlonal contacts 25I and 252 are provided to which load circuits may be connected to be controlled by the operation of the armatures 245 and 246. Connections similar to those shown in Figs. 1 and 2 are provided by which the contact gaps 231 and 236 of .the D'Arsonval relay control the supply of power to the coils 243 and 244 of the latch relay from a Thus starting from the negative terminal of the battery 265 a circuit extends through the normally open contact gap 231 of the DArsonval relay through the contact gap 254 which is operated by the armature 246 of the latch relay, thence through the coil 243 and its shunt resistor 261 and thence through the resistor 233 to the positive terminal of the battery 265. A part of the current is shunted around the resistor 233 to flow through the photoelectric cell 23l, the coil 2l5 of the D'Arsonval relay and the resistor 234. Similarly, a circuit extends from the negative terminal of the battery 265 to the normally closed contact gap 236 of the D'Arsonval relay, to the contact gap 253 of the latch relay through the coll 244 and its shunt 268 and through the resistor 234 back to the battery 265. Part of the current is shunted around the resistor 234 to flow through the coil 2l5 .of the DArsonval relay, the'photoelectrlc cell 23! and the resistor 233. The circuit connections thus far described correspond to those of Figs. 1 and 2.

Inaddition to the connections just described, cross connections are provided between the two separate coil circuits just traced to permit the two coils 243 and 244 to be energized simultaneously. Thus a circuit path is provided which may be traced as follows: Beginning at the negative terminal of the battery 265, it extends through the normally open contact gap 231 of the DArsonval relay thence through a cross connection cons sting of a resistor 241 and the contact gap 255 and thence through the coil 244 of the latch relay and the resistor 234 to the positive terminal of the battery 265. This permits the coil 244 as well as the coil 243 to be energizedunder control of the contact gap 231 of the DArsonval relay. A similar additional circuit extends from the negative terminal of the battery 265. through the normally closed contact gap 236 of the DArsonval relay, thence through a cross connection consisting of a resistor 248 and the contact gap 256,

' and thence through the coil 243 of the latch relay and the resistor 233 to the positive terminal of the battery 265.

The system of Figs. 5 and 6 operates as follows:

Assume that the photoelectric cell 23l is sufiiciently illuminated so that the contact gap 236 is open and that the latch relay 246 has its armatures 245 and 246 in the positions shown in Fig. 5. In this position of the armatures 245 and 246, the contact gaps 255 and-254 are open so that neither the coil 243 nor the coil 244 of the latch relay may be energized by closing the contact gap 231 of the DArsonval relay. However, the contact gaps 256 and 253 both are closed so that the contact gap 236 of the DArsonval relay may, close to energize both of the coils 243 and 244. The coils 243 and 244 have approximately equal resistances. as do the resistors 261 and 266. Because the current path throughthe coil 243 includes the re- 233 and 234 are substantially'equal in value so that the voltage drop across the resistor 234 will be higher than that across the resistor 233. The difierence of these two voltage drops will cause an energy transfer" component of current to transverse the coil 2l5 of the DArsonval relay in the direction opposite to the direction of the photoelectric current. This causes the coil 215 to increase the contact pressure at the gap 236K The coil 243 of the latch relay 246 attracts the armature 245 so as to take up the slack in the latch mechanism and remove the frictional drag from the armature 246. The energized coil 244 causes the armature 246 to pick-up and in so doing, to open the contact gap .256 to ole-energize coil 243. It, also, closes the contact gap 254 in preparation for a subsequent operation of the contact gap 231. The de-energizing of the coil 243 by the opening of the contact gap 256 removes one component of current from the coil 2l5 of the DArsonval relay and in so doing causes a still further increase of contact pressure at the contact gap 236 of the DArsonvalrelay 2).

The closing of the contact gap 254 does not complete a circuit because both the contact gaps 231 and 255 are open. Upon opening the contact gap 256, the supply of power from the battery 265 to the coil 243 is interrupted. Thereupon the magnetic field begins to collapse, but this collapse is retarded by a current which circulates through the coil 243 and its shunt resistor 26?. The retarding of the collapse of the magnetic field delays the release of the armature 245 for a periodof time after the operation of the armature 246. When the flux of the magnet of the coil 243 reaches a sufiiciently low value, the armature 245 releases and in so doing opens the contact gap 253 to interrupt the flow of current to the coil 244, and it, also, closes the contact gap 255 in preparation for a subsequent operation of contact gap 231. It, also, operates the load contacts 25!. This leaves the system drawing no current from the battery 265 and with the system no longer responsive to any opening or closing of the contact gap 236. This removes the energy transfer current component from the current of the coil 2l5. It is thus seen that by the use of the resistors 241 and 246, I have succeeded in embodying my present invention with the time delay system of my co-pendi'ng application already referred to. Inasmuch as the particular coil which is energized through one of these re- .sistors is, in every case, already substantially in its drawn-up position so that it is not necessary to supply it as much power as is supplied to the other coil whose armature is in the released position at the time.

Subsequently, the normally open contact gap 231 of the DArsonval relay may close to energize both coils of the latch relay and to execute a time delay between the closing of the contact gap 231 and the operation of the load contact 252 of the armature 246.

Fig. '1 illustrates a relay system embodying my present invention in a modification of the system of Fig. 5 wherein the D Arsonval relay responds to the voltage of the battery or other power supply which operates the relay. The circuit is more simply shown in the across-the-line diagram of Fig. 8. Fig. 8 depicts only the circuit relationships between the various elements and makes no attempt to diagrammatically represent any mechanical relationshipsbetween t; am. A comparison of Fig. 8 with Fig. 6 will show that paths consisting of the resistor 334 and the coil 3l5 of the DArsonval relay and of the resistor 333 and the resistor 310 respectively and-thence through the resistor 3' to the negative terminal of the battery. Preferably the resistor 310 has a resistancevalue approximately equal to the resist'ance of the DArsonval relay coil 3l5. Generally the resistance 3 will be very high compared to the other resistances of the system. Inasmuch as the DArsonval relay coil 3|5 receives its current from a fixed resistance system (assuming that no' current flows through the relay coils 343 and 344), the value of current flowing therein is directly proportional to the voltage of the battery 365.

When the normally closed contact 338 of the DArsonval relay closes, current is drawn through both of the coils 343 and 344 in the manner described in connection with the system of Fig. 5, the greater current being drawn by coil 344. This causes an additional component of current to flow through the coil 3l5 in the direction opposite to that in which current already was flowing so as to decrease the net current in the relay 3l5. This results in increased contact pressure at the contact gap 338 to aid the operation 0! the DArsonval relay. Similarly when the normally open contact gap'33l of the DArsonval relay closes, it energizes both of the coils 343 and 344 drawing the greater current through the coil 343 so that the voltage drop across the resistor 333 is greater than the drop across the resistor 334. This causes an increase of the total cur rent in the DArsonval relay coil 3I5 in the same manner as was described in connection with the system of Figs. 5 and 6 so as to improve the operation of the contact gap 331 of the DArsonval relay.

In the system of Figs. 7 and 8, the battery which supplies the power for the latch relay coil has become the primary control device of the system. It is immaterial that the current drawn by the coils of the latch relay may impair the voltage of the battery during the time that those coils are drawing current, because at that particular time the measure of response of the DArsonval relay to the battery voltage is purposely disturbed by the introduction of energy transfer current for the purpose of improving the action and operation of the contacts of the D'Arsonval relay. Inasmuch as power is drawn from the battery 365 by the coils of the latch relay, only during the brief interval that is required for the operation of the armatures thereoi, the voltage of the'battery will be disturbed thereby only during that brief operating period and the DArsonvalrelay will respond accurately to the battery voltage at all times when it is not producing an operation of the latch relay. The

- system of Figs. 7 and 8 conveniently may be employed for controlling a system in which the battery v ltage indicate: the operation which is required, as for example: In a system for automatically charging a storage battery.

While I have shown and described various specific embodiments of my present invention, it will be apparent to those skilledin the art that the same are by way of representation only, and that the invention is capable of various modifications and variations. Therefore, I do not wish to be limited except by the scope claims.

I claim:

l. A relay of the DArsonval type having a coil and a pair of cooperating contacts, primary control means for supplying current to said coil for controlling and operating the relay, a power-supply separate from said primary control means, at least one load circuit for said relay comprising said contacts and said power supply, connections therefrom to the coil of the relay for supplying of the appended current from said power supply to said relay coil equal in magnitude but opposite in direction to the change caused by said closing operation of said contacts.

2. A relay having a coil and contacts, a power supply, a load circuit for said relay including said contacts and including said power supply, means comprising connections between said load circuit and the coil of the relay for supplying current from said power supply to said relay coil in response to an operation of said contacts, the power supply being so connected as respects the polarity thereof that when said contacts execute said operation thereof the change of current caused thereby in the relay coil is such as to increase the tendency of the relay to maintain thecontacts in their operated condition, and means in said load circuit operable in response to said operation of the relay contacts for causing a change in the coil current of the relay substantially equal in magnitude but opposite in direction to the change caused by the operation of the contacts.

3. A relay of the DArsonval type having a coil and having contacts which provide two contact gaps which cannot close simultaneously, a power supply, a load device, circuit connections between said contacts, power supply, load device and the coil of the relay such that said load device is responsive to a closing of only one of said contact gaps and such that when that one contact gap closes it causes the power supply to operate said load device and to deliver current to said relay coil in such direction as to increase the pressure between the engaged contact surfaces of said contacts, said load device being operable in response to the closing of said one contact gap of the DArsonval relay to substantially interrupt the flow of current through the closed contacts. to substantially interrupt the flow of current from said power supply to said relay coil, to render said load device unresponsive to any further operation of said one contact gap, and to render said load device responsive to a closing operation of the other of said contact gaps.

4. A control relay having a coil and having contacts which provide two contact gaps which close at different values of current in said coil, 2. second relay having a coil and contacts, a power supply, first connections including the two contact gaps of the control relay, the coil and contacts of the second relay and the power supply for adapting said second relay to energize and operate when one contact gap of the control relay closes and for adapting said second relay to deenergize and operate when the other contact gap of the control relay closes, and other connections between said first connections and the coil of the control relay for (1) supplying current from said power supply to said coil of the control relay, for (2) producing a change in the current in said coil of the control relay when each contact gap thereof closes to operate said second relay, said change beng in such a direction as to tend to aid the closing of the contact gap, and for (3) causing a substantially equal but opposite change in said current when the second relay operates in response to the closing of said contact gap of said control relay.

' 5. A relay of the DArsonval type having a coil and having contacts which provide two contact gaps connected in series which close at different values of current in said coil, a second relay having a coil and having contacts providing a contact gap which closes when the coil of said second relay is energized, a power supply, said contact gap of said second relay being connected to the coil of said second relay, said contact gap and coil of said second relay and said power supply being connected in series, said series connected contact gaps of the DArsonval relay being connected across the series connected contact gap and coil of said second relay, and connections including the coil of the DArsonval relay between (1) the connection between the two contact gaps of'the DArsonval relay and (2) the connection between the coil and contact gap of the second relay.

6. A control relay having a coil and having contacts which provide two contact gaps which close at different values of current in said coil, a latch relay having two interfering armatures each of which has both a drawn up and released position, each of which when in its own released position latches the other in its drawn up position, separate magnet coils for operating said armatures, contacts which provide a separate contact gap operated by each of said armatures, each of said separate contact gaps being arranged to be open when the armature operating it is in the released position and to be closed when the armature operating it is in the drawn up position, a power supply, circuit connections for supplying power from said power supply to the magnet coil associated with ach of said armatures through a contact gap operated by the other armature and through one of the contact gaps of the control relay, and other connections between the coil of said control relay and the first mentioned. circuit connections for supplying power fromsaid power supply to the coil of the control relaysimultaneously with the supplying of power to either of the magnet coils ofthe latch relay.

7. A control relay. having a coil and having contacts which provide two contact gaps which operate at different values of current in said coil, a latch relay having two interfering armatures each of which has both a drawn-upand 9. released position, each of which latches the other in one of the two positions thereof, separate magnet coils for operating said armatures, contacts which provide a separate contact gap operated by each of said armatures, a power supply, circuit connections for supplying power from said power supply to the magnet coil of each of said armatures under the concurrent dependent control of the contact gaps of a dependent control group consisting of a contact gap operated by the other armature and one of the contact gaps of the coil of said control relay and the first mentioned circuit connections for supplying power from said power supply to the coil of the control relay under the concurrent independent control of either dependent control group.

8.'A control relay having a coil and having contacts which provide two contact gaps which operate at different values of current in said coil, a latch relay having two interfering armatures each of which has both a drawn-up and 8. released position, each of which latches the other in one of the two positions thereof, separate magnet coils for operating said armatures, contacts which provide a separate contact gap operated by each of said armatures. a power supply, circuit connections for supplying power from said power supply to the magnet coil associated with each of said armatures under the concurrent dependent control of a contact gap operated by the other armature and one of the contact gaps of the control relay, and other connections between the coil of said control relay and the first mentioned circuit connections for supplying power from said power supply to the coil of the control relay under the control of the contacts of said control relay.

9. A control relay having a coil and having contacts which provide two contact gaps which close at different values of current in said coil, a latch relay having two interfering armatures each of which has both a drawn-up and a released position, each of which when in its own released position latches the other in its drawn-up position, separate magnet coils for opera, .ig said armatures, contacts which provide a separate contact gap operated by each of said armatures, each of said contact gaps being arranged to be open when the armature operating it is in the released position and to be closed when the armature operating it is in the drawn up position, a power supply, two resistors, two circuits each of which includes (1) the magnet coil of one of said armatures, (2) said contact gap operated by the other armature, (3) one of said resistors, (4) one of the contact gaps of the control relay and (5) the power supply; and means including a connection between each resistor and the coil of the control relay for shunting current around said resistor through said coil of the control relay.

10. In combination, a DArsonval relay having a coil and two contact gaps which close at diiferent values of current in said coil, a latch relay having two interfering armatures each of which has both a drawn-up and a released position, each of which when in its own released position latches the other in the drawn-up position thereof, separate magnet coils for operating said armatures, contacts which provide separate contact gaps operated by each of said armatures, each of said contact gaps being arranged to be open when the armature operating it is in the released position and to be closed when the armature operating it is in the drawn up position, a power supply, two resistors, two load circuits for said DArsonval relay each of which includes (1) the magnet coil of one of said armatures of the latch relay, (2) a contact gap operated by the other of said armatures, (3) one of said resistors, (4) one ofthe contact gaps of the DArsonval relay and (5) the power supply; and a coil circuit for the coil of the DArsonval relay including both said resistors and the coil of the D'Arsonvalrelay.

11. In combination, a DArsonval relay having a coil and having, also, contacts providing two contact gaps which close at different values of current in said coil, a latch relay having first and second armatures each of which has a drawn up and a released position, each of which is adapted when in its own released position to latch the other in the drawn-up position, first and secondmagnet coils for operating said first and second armatures respectively, contacts providing first and second contact gaps operated by said first and second armatures respectively, each of said first and second contact gaps being arranged to be open when the armature operating it is in the released position and to be closed when the armature operating it is in the drawn up position, a power supply, first, second, third and fourth resistors, and circuit connections between the aforementioned elements to provide the following four circuit paths: (1) a circuit path including the power supply, one contact gap of the D'Arsonval' relay, the second contact gap of the latch relay, the first coil of the latch relay and the first resistor; (2) a circuit path including the power supply, the other contact gap of the D'Arsonval relay, the first contact gap of the latch relay, the second coil of the latch relay and the second resistor; 3) a circuit path including the power supply, the third resistor, the coil of the DArsonval relay and the second resistor; and (4) a circuit path including the power supply, the third resistor, the fourth resistor and the first resistor.

12. In combination, a DArsonval relay having a coil and having, also, contacts providing two contact gaps which close at different values of current in said coil, a latch relay having first and" second armatures each of which has a drawn up and a released position, each of which is adapted when in its own released position to latch the other in the drawn up position, first and second magnets and coils therefor for operating said first and second armatures respectively, each of said magnets including means for opposing and retarding the collapse of the magnetic fiux thereof, contacts providing first and second contact gaps operated by said first and second armatures respectively, each of said first and second contact gaps being arranged to be open when the armature operating it is in the released position and to be closed when the armature operating it is in the drawn up position, contacts providing third and fourth contact gaps operated by said first and second armatures respectively, each of said third and fourth contact gaps being arranged to be closed when the armature operating it is in the released position and to be open when the armature operating it is in the drawn up position, a power supply, first, second, third and fourth resistors, circuit connections between the aforementioned elements to provide the following four circuit paths: (1) a circuit path including the power supply, one contact gap of the DArsonval relay, the second contact gap of the latch relay, the first coil of the latch relay and the first resistor; (2) a circuit path including the power supply, said one contact gap of the DArsonval relay, the fourth resistor, the third contact gap of the latch relay, the second coil of the latch relay and the second resistor; (3) a circuit path including the power supply, the other contact of the DArsonval relay, the first contact gap of the latch relay, the second coil of the latch relay and the second resistor; and (4) a circuit path including the power supply, said other contact of the DArsonval relay, the third resistor, the fourth contact gap of the latch relay, the first coil of the latch relay and the first resistor; and connections between (1) said first and second resistors and (2) the coil of the D'Arsonval relay, such that a change of current in either said first or said second resistor produces an accompanying change of current in the coil of the DArsonval relay.

13. In combination, a control relay having a coil and contacts providing two contact gaps, a control circuit including said coil, connections to said control circuit for supplying current thereto, a primary control device in said control circuit for supplying current to said coil for controlling and operating the control relay, which primary control device presents a non-symmetrical impedance to electrical potential differences impressed thereon such that a greater proportion of the current supplied to said circuit through said connections traverses said coil when current so supplied to said control circuit traverses said coil in one direction than when said current traverses said coil in the other direction, a direct current power supply separate from said primary control device, load circuits for said control relay including said power supply and said contact gaps, means for supplying current from said power supply to said control circuit to pass current in one direction through said coil under control of one of said contact gaps and in the other direction under control of the other of said contact gaps, said means including said load circuits and including, also, said connections to said control circuit, said connections to said control circuit including means for controlling the relative magnitudes of the currents supplied in opposite directions through said connections, and for passing the greater current in the direction therethrough which produces a current through said coil of said control relay in the direction in which said coil receives the smaller proportion of the current supplied through said connections.

14. In combination, a control relay of the D'Arsonval type having a coil and having, also, contacts which provide first and second contact gaps, said contact gaps being connected in series and adapted to close at different values of current in said coil, a control circuit including said coil, first connections to said circuit for supplying current thereto, a primary control device in said circuit for supplying current to said coil for controlling and operating said control relay, which primary control device presents a non-symmetrical impedance to electrical potential differences impressed thereon such that a greater proportion of the current supplied to said circuit through said first connections traverses said coil when said current passes-through said coil in the direction required for closing said first contact gap and for increasing the contact pressure thereof than when said current passes through said coil in the direction required for closing said second contact gap and for increasing the contact pressure thereof, a second relay having 'a coil and having a contact gap which closes when its coil is energized, a direct current power supply separate from said primary control device, said contact gap of said second relay being connected to the coil of said second relay, said contact gap and coil of said second relay and said power supply being connected in series, said series connected gaps of the D'Arsonval relay being connected across the series connected contact gap and coil of the second relay with said first contact gap of the DArsonval relay connected to the contact gap of said second relay, said first connections being connected between (1) the connection between the two contact gaps of the DArsonval relay and (2)the connection between the coil and contact gap of the second relay, said first connections being so arranged with respect to the polarity of said direct current power supply that when said first contact gap of said DArsonval relay closes, current from said power supply traverses the coil of the DArsonval relay in the direction required for increasing the contact pressure of said first contact gap of said DArsonval relay. 5

KARL H. s01 .MERMEYER. 

